Method and arrangement for sound-suppression in wheels

ABSTRACT

A method and a device for sound suppression, in wheels, of natural frequency sound originating from an air cavity which is inside the wheel between the tire and the rim, which includes at least one resonator arranged inside the wheel. The resonator is designed for the suppression of sound resulting from the natural frequency of the wheel and is preferably formed of four quarter-wave resonators or of Helmholtz-resonators.

BACKGROUND OF THE INVENTION

The present invention relates to a method and an arrangement forsound-suppression in wheels in accordance.

A person who is in the passenger compartment in a motor vehicle oftenexperiences that he/she is in a noisy environment. The noise level,however, varies depending on the size and manufacture of the vehicle oneis sitting in. It is also obvious that noise increases when the vehicleaccelerates. A common inference is therefore that the noise principallycomes from the engine. However, it is so that a relatively large amountof the noise inside the passenger compartment originates from roadnoise. In modern cars a great deal of effort has been applied tominimize the engine noise which penetrates into the passengercompartment and also road noise but there still remains a lot when it isa question of the latter. Minimizing the noise from the road and thewheels is moreover becoming more important as the engine noise decreasesbecause the noise from the road and wheels in this case, relativelyseen, forms a larger part of the total noise in the passengercompartment.

The noise which is usually attributed to the wheels of the vehiclecomprises partly the external noise which is produced when a wheel meetsthe road surface and partly the sound which is produced in the aircavity inside the wheel because of a standing wave being excited whichis based on the natural frequency (resonance frequency) of the wheel.Thus there occurs what can be described as a resonance tone inside thewheel. The natural frequency of the wheel is determined by thecircumference in such a way that the circumference of the internal aircavity is equal to one wave length. The bigger the wheel, i.e. thebigger the circumference, the longer the wave length and therewith thelower the natural frequency. A 15″ wheel has a natural frequency ofapproximately 230 Hz. The frequency interval which is of interest inthis connection is from approximately 250 Hz down to just under 100 Hz,where the latter corresponds to a truck wheel. The external noise whichbelongs to the meeting of the tire with the road surface depends e.g. onthe appearance of the tire, the pattern of the tread and the material ofthe tire, as well as the road surface. This noise is airborne. The noisewhich occurs inside the wheel as a result of resonance vibration is to acertain degree airborne but to the greatest part it is a sound body,i.e. the sound propagates via the wheel suspension and further into thepassenger compartment of the car.

The object of the present invention is to suppress there so-callednatural frequency sounds in wheels which originate in the air cavityinside the wheel.

Devices for suppressing sound inside wheels are known from EP-A-0 663306 and JP-A-07 052 616. From these documents it is known in the priorart to suppress sound inside wheel cavities by quite simply placing asound-absorbing material there. The effect of this must be considered tobe extremely limited. In EP-A-0 663 306 is mentioned e.g. that theinvention is to suppress noise which originates from the naturalvibrations in the wheel cavity and, as an example, natural frequenciesfrom 150 to 250 Hz are mentioned. In the last mentioned document it isalso shown how resonators can be arranged in connection to the soundabsorbers inside the tire. These resonators are, however, intended toabsorb sounds other than natural frequency sound, as their design issuch that their dimensions limit sound suppression to frequencies of theorder of 1000 Hz, which greatly exceed the natural frequency of avehicle wheel. As mentioned, the natural frequency is determined by thecircumference of the wheel. A natural frequency of 1000 Hz wouldcorrespond to a wheel with a diameter of approximately 11 cm.

The use of resonators for sound suppression in wheels is in itself alsoknown from EP-B-0 041 127 and EP-A-0 665 529. In the first of thesedocuments the resonator is on a sound shield which is placed on theoutside of the wheel. In the second of these documents resonators areplaced in the wheel housing. Both these documents therefore show soundsuppression of external airborne sound originating from the wheel'scontact with the ground. Neither of these documents treat the problem ofbody-transmitted sound depending on the natural vibrations inside thewheel.

Finally, in order to illustrate the prior art, JP-A-487 803 ismentioned, from which document it is known to half the wave length andthereby double the resonance frequency inside a wheel by producing anintermediate wall inside the wheel. The resulting double frequency isnot experienced to be equally noisy as the original frequency. Here,however, it is not a question of sound suppression in a strict sense.

SUMMARY OF THE INVENTION

The problem of suppression of natural frequency is solved according tothe present invention by a method and arrangement which includesproviding at least one resonator inside the wheel, the resonator beingdesigned for suppression of second resulting from the natural frequencyof the wheel.

The advantage of the present invention as it is defined in theindependent claims is that a considerably more effective suppression ofnoise originating from the wheel cavity is obtained than is the caseaccording to the prior art. By using resonators, sound with thefrequency which the resonators are tuned to is in principle completelyextinguished. Through this sound suppression, the comfort for the driverand the passengers who are in the cabin space of the vehicle isimproved. A lower sound level has also the advantage that it leads toimproved safety because one quite simply becomes tired from being in anoisy environment.

Consequently, by means of the invention, a sound-suppression device isobtained which is effective and easily can be adapted to different wheeldimensions. The invention has furthermore the advantage that alsoseveral frequencies can be suppressed by using several resonators, tunedto different frequencies. In this way, there is the possibility to usethe same arrangement for several wheel dimensions without requiringindividual adaptation. There is also the possibility of integrating thesound-suppression device in the wheel on or in the tire itself. No loosedevices are needed in this case, which signifies a further advantage.

Other features and advantages of the present invention will becomeapparent from the following description of the invention which refers tothe accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in detail with reference to a numberof embodiments illustrated in the accompanying drawings, in which:

FIG. 1a shows a sketch of the principles of the arrangement according tothe invention,

FIG. 1b shows a sketch of the principles where the length of theresonators varies.

FIG. 1c shows a sketch of the principles where the length of theresonators varies in a different way to that in FIG. 1b,

FIG. 1d shows a sketch of the principles where the resonators vary in away different to that of FIG. 1b.

FIG. 1e shows a sketch of the principles where the resonators vary inyet another way different to that of FIG. 1b,

FIG. 1f shows a sketch of the principles of how the wave length for thefrequency is influenced by the rotation of the wheel,

FIG. 2 shows a sketch of the principles of a first embodiment of thedevice according to the invention,

FIG. 3 shows a detail view of the embodiment according to FIG. 2, seenfrom below and in section,

FIG. 4 shows the arrangement in FIG. 2 when it is used in such a waythat it is fixed in the bottom of the rim,

FIG. 5 shows a perspective view of a second embodiment of the deviceaccording to the invention,

FIG. 6 shows a detail view of the arrangement in FIG. 5, in section seenalong the line VI—VI,

FIG. 7 shows a third embodiment of the arrangement according to theinvention seen in section,

FIG. 8 shows a sketch of the principles of a fourth embodiment of thearrangement according to the invention, and

FIG. 9 shows a sketch of the principles of a fifth embodiment of thearrangement according to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

The principle of the invention is shown in FIG. 1a. A vehicle wheel 1comprises a tire 2 and a rim 3. Inside the wheel is a cavity 5 (FIG. 4)filled with air, more precisely between the bottom 7 of the rim 3 andthe inside of the tire 2. This cavity extends around the whole of thewheel and has a mean diameter with reference numeral Ø_(M). When thewheel meets the road surface, a standing wave with a resonance frequencywhich is specific for the wheel and which is determined by the diameterof the wheel will be excited inside this air cavity. As an example itcan be mentioned that a 15″ wheel has a mean diameter Ø_(M), for the aircavity of approximately 47 cm and a circumference of 148 cm. A soundwave length of λ=148 cm corresponds to a first resonance in the cavityof f_(r)=230 Hz.

However, with increasing rotational velocity of the wheel, twooppositely travelling sound waves are produced which consequently havedifferent lengths of path, one being shorter than 148 cm and the otherlonger than 148 cm. This means that a wheel which rotates has twonatural frequencies, one on each side of f_(r)=230 Hz. The principle ofthis is illustrated in FIG. 1f. The letter A denotes the contact pointbetween the wheel and the ground at the time t. If the wheel rotateswith the rotational direction which is shown by the arrow E, the contactpoint between the wheel and the road surface at the time t+1 will be atB. From this follows that the wave length λ₁ for the resonance tonewhich is excited in the direction opposite to the rotational directionof the wheel is longer than the wave length λ₂ for the resonance tonewhich is excited in the rotational direction of the wheel.

In order to extinguish the resonance sound already inside the wheel, thewheel is provided with a hose which is placed inside the wheel and whichis divided by means of intermediate walls into four sections10,11,12,13, wherein each section corresponds to ¼ wave length. Eachhose section is provided with an opening at one end and directed towardsthe cavity, whereby four so-called quarter-wave resonators are obtained.

A quarter-wave resonator functions so that the reflected sound will bein anti-phase to the incident sound, wherein the sound is quite simplyextinguished.

FIG. 1a shows the principle case where the four quarter-wave resonatorsare equally long. In order to also be able to extinguish sound, inaccordance with that which has been discussed above for increasedrotational speed, originating from two ground resonances, the fourquarter-wave resonators can be made pair wise equally long. In FIG. 1b asketch of the principles for this case is shown. From the Figure isevident that two of the resonators 11 b, 13 b are made somewhat shorterthan a quarter-wave length based on the mean diameter Ø_(M), i.e. in theexample described, somewhat shorter than Ø_(M)=47/4 cm, and the othertwo resonators 10 b, 12 b are made somewhat longer. It would also beconceivable to let the resonators partially overlap if it is considerednecessary to have longer resonators.

It is obviously also conceivable to make the resonators of varyinglength to be able to extinguish sound within a somewhat larger regionaround the resonance frequency which is based on the mean diameter Ø_(M)of the wheel, and which thus corresponds to greater variations in therotational speed of the wheel. One example of such an embodiment isshown in FIG. 1c. From the Figure can be seen that the resonator 13 c ismade somewhat shorter than a quarter-wave length based on the meandiameter Ø_(M) of the wheel, i.e. in the described example somewhatshorter than Ø_(M)=47/4 cm, that the resonator 12 c is made evenshorter, i.e. is tuned for an even higher frequency, that the resonator10 c is made somewhat longer than a quarter-wave length and that theresonator 11 c is made even longer. i.e. is tuned for an even lowerfrequency. When the resonators are designed so that each of them isadapted to a special natural frequency, only one or two of them willfunction at a time, i.e. at a certain rotational speed of the wheel. Theothers will come into function as the speed of rotation changes. Inaddition, in this way, to be able to extinguish natural frequency soundswithin a large interval or one and the same wheel, it is also possiblein this way to use an arrangement with the same set of resonators forwheels with different tire dimensions, e.g. both for 15″ tires and 16″tires.

As an alternative to having resonators separated from each other andletting each have its own opening, which is the case in FIGS. 1a-1 c, itis conceivable to leave out the partition wall between two resonatorsand instead have a single opening situated where the partition wall wasearlier situated, whereby this opening replaces the earlier twoopenings. In this way, two quarter-wave resonators are obtained, one ineach direction seen from the opening. This alternative is illustrated inFIGS. 1d and 1 e. The arrangement in FIG. 1d corresponds to thearrangement in FIG. 1a as to size, frequencies and general function ofthe resonators, while the device in FIG. 1e corresponds to thearrangement in FIG. 1b. Naturally, it would also be conceivable toperform the corresponding modifications of the device in FIG. 1c, but aseparate Figure of this has not been included.

As to the following examples of embodiments, they can, of course, alsobe modified so that any of all the alternative principles above can beapplied.

A first embodiment of the invention is shown in FIG. 2. It comprises asuppression arrangement in the form of a hose 9 divided into fourresonators 10,11,12,13. The resonators are separated by intermediatewalls 15,16,17,18 arranged inside the hose 9. Each resonator is providedat the one end with an opening 20,21,22,23 facing towards the air cavityinside the wheel. FIG. 3 shows a detail of the arrangement in FIG. 2 insection. Here we can see the resonator 10 with its opening 23 and theresonator 13. Between the resonators 10,13 there is an intermediate wall18. The end of the resonator 13 abutting the end of the resonator 10provided with an opening, is preferably at its base provided with aninternal damper 19 in the shape of a sound-absorbing material next tothe intermediate wall 18. This damper has been arranged in order tocover a somewhat wider frequency interval which, for example, can bedesirable because of frequency changes dependent on changes in speed.

The hose is advantageously manufactured from a somewhat flexiblematerial permitting it to be forced onto the rim. Examples of suitablematerials are rubber, preferably of a relatively stiff type, plastic ormetal.

The arrangement shown in FIGS. 2 and 3 can advantageously be designed tobe fixed in the bottom of the rim of the wheel which is to be dampened.An example of this is shown in FIG. 4. Normally no special design of therim is required, but the hose is fixed by e.g. gluing or a similar way.It can also be sufficient to optimize the hose for forcing on so thatafter it has been forced into place, it is fixed. If necessary, however,the bottom of the rim 7 can have a special design to facilitate thefixing of the hose 9.

FIGS. 5 and 6 show a second embodiment of the arrangement according tothe invention. The hose has here been exchanged for a channel 25 whichis arranged on the rim 26, more closely defined, on the bottom 27 of therim. This channel extends around substantially the whole of thecircumference of the bottom of the rim. The channel can either becompletely integrated into the rim or, as shown in FIGS. 5 and 6,consist of a wall 28 arranged on the bottom 27 of the rim, wherein thespace between the edge 29 of the rim and this wall is closed by means ofa lid 30 in order to form the channel 25. This lid may possibly need tobe provided with some type of damper. The channel 25 is, in the same wayas in the first embodiment and in accordance with the sketch in FIG. 1a,divided into four resonators, each provided with an opening at one end,of which only one resonator opening 31 is actually shown. In the otherend, i.e. the bottom of the resonator, the channel is closed by an endwall 38 and is preferably provided with a porous absorbent 32 with thesane purpose as before.

FIG. 7 shows a third embodiment of the arrangement according to thepresent invention. Here we can see a rim 40 on which a tire 41 ismounted. On the inside of the tire 41, i.e. the side which is oppositeto the tread 42 and which is facing in towards the cavity 43 which isformed between the rim and the tire, there is a channel 45. This channelcorresponds to the channel 25 in the second embodiment and the hose 9 inthe first embodiment and extends consequently around essentially thewhole of the internal circumference of the tire. The channel 45 isconsequently divided into four resonators which are designed in the sameway as the quarter-wave resonators in the channel 25 and in the hose 9.The holes of the resonators face in towards the cavity. The channel canbe vulcanized fast onto the inside of the tire or already duringmanufacturing of the tire be integrated into the inside of the tire.Naturally. the channel can also be placed somewhere else on the insideof the tire than opposite the tread (as in the illustrated embodiment),depending on what is appropriate from case to case.

In FIG. 8 a fourth embodiment of the invention is shown. The Figureshows a vehicle wheel 50 in section and here two channels formingquarter-wave resonators 51, 52 are arranged on the inside of the rimwall 55. The resonators are preferably integrated into the rim. They aredesigned in the same way as earlier quarter-wave resonators, i.e. withan opening 53 and 54, respectively, at one end and preferably with aninternal damper 56, 57 in the shape of a porous absorbent in the bottom,i.e. the other end. In this embodiment it could also be possible,instead of forming the resonators as quarter-wave resonators, to formthem as Helmholtz-resonators in analogy with FIG. 9 below.

Finally, a fifth embodiment is shown in FIG. 9. According to thisembodiment, quarter-wave resonators as well as Helrnholtz-resonators canequally be used. The Figure shows a vehicle wheel 60 in section. The rim61 is provided with spokes 62. Inside at least one, and preferably more,of the spokes, there are cavities 63 with openings 64 arranged accordingto the principle for a quarter-wave resonator or a Heimholtz-resonatorwith volumes tuned for the resonance frequency(ies) which the actualwheel dimension gives rise to. The Figure shows four cavities shaped asHelmholtz-resonators. Also here the resonators are advantageouslyintegrated in the rim.

The above description of different embodiments of sound-suppressionarrangements according to the invention are only to be considered to beexamples of the invention, and the inventive concept is not to belimited to this but the invention can be varied within the scope of thefollowing patent claims. It must be especially emphasized that in allthe embodiments each resonator can be shaped and dimensionedindividually so that each separate resonator is tuned for the damping ofa specific frequency; alternatively the resonators can be dimensionedpair wise the same. It is also conceivable to modify all the embodimentsso that also Helmholtz-resonators can be used. Furthermore, theinvention is not be considered limited to motor vehicles but can also beapplied to wheels for other types of vehicles, where correspondingproblems occur.

What is claimed is:
 1. Method for the suppression in wheels of naturalfrequency noise originating from an air cavity inside the wheel,comprising arranging at least one quarter-wave resonator inside thewheel, the resonator being designed to communicate with said air cavityfor suppression of sound resulting from the natural frequency of thewheel.
 2. Method according to claim 1, wherein the resonator isintegrated into the wheel.
 3. Method according to claim 1, wherein thewheel comprises a rim and the resonator is arranged in the rim. 4.Method according to claim 1, wherein the wheel comprises a tire and theresonator is arranged in the tire.
 5. Device for suppression in wheelsof natural frequency sound originating from an air cavity inside thewheel, which comprises at least one quarter-wave resonator arrangedinside the wheel, the resonator being designed to communicate with saidair cavity for the suppression of sound resulting from the naturalfrequency of the wheel.
 6. Device according to claim 5, wherein thewheel comprises a tire and a rim, and the resonator comprises achannel-shaped device which is arranged inside the wheel in a cavitywhich is formed between the tire and a rim of the wheel.
 7. Deviceaccording to claim 6, wherein the channel-shaped arrangement has a totallength corresponding to a wavelength of the natural frequency sound ofthe wheel, and includes partition walls arranged inside the channel fordividing the channel into four channel sections, each being providedwith an opening facing towards the wheel cavity and each forming aquarter-wave resonator for suppression of the natural frequency sound ofthe wheel.
 8. Device according to claim 7, wherein each of the channelsections is essentially of equal length.
 9. Device according to claim 7,wherein the four channel sections are arranged in pairs, the twosections in each pair being essentially equally long and each pair beingdimensioned for suppression of natural frequency sound of the wheel ofone of essentially two frequencies resulting from two sound-wavestraveling in opposite directions which occur when the wheel rotatesagainst a surface.
 10. Device according to claim 7, wherein the fourchannel sections have different lengths for suppression of naturalfrequency of sound of essentially four different frequencies of thewheel resulting from two sound waves traveling in opposite directionsand at two different rotational speeds which occur when the wheelrotates against a surface.
 11. Device according to claim 6, wherein thechannel-shaped arrangement has a total length corresponding to onewavelength of the natural frequency sound of the wheel and includespartition walls arranged inside the channel for dividing the channelinto two channel sections each being provided with an opening facingtowards the wheel cavity, and each forming two quarter-wave resonatorsfor the suppression of the natural frequency sound of the wheel. 12.Device according to claim 11, wherein the openings of the respectivechannel sections arc arranged substantially in the middle of the channelsections so that each channel section forms two quarter-wave resonators,one in each direction, as seen from the opening, wherein thechannel-shaped arrangement is divided into four essentially equally longquarter-wave resonators for the suppression of the natural frequencysound of essentially one frequency.
 13. Device according to claim 11,wherein the openings of the respective channel sections are arrangedsubstantially near the middle of the channel section so that eachchannel section forms two quarter-wave resonators, one in eachdirection, as seen from the opening, and are arranged in pairs which areessentially equally long and are dimensioned for the suppression of thenatural frequency sound of essentially two frequencies of the wheelresulting from two sound-waves traveling in opposite directions whichoccur when the wheel rotates against a surface.
 14. Device according toclaim 11, wherein the openings of the respective channel sections arearranged near the middle of the channel section so that each channelsection forms two quarter-wave resonators, one in each direction, asseen from the opening, whereby the two quarter-wave resonators aresomewhat different in length and are dimensioned for the suppression ofthe natural frequency sound of essentially four different frequencies ofthe wheel resulting from two sound-waves traveling in oppositedirections and at two different rotational speeds which occur when thewheel rotates against a surface.
 15. Device according to claim 6,wherein the channel-formed arrangement is a hose.
 16. Device accordingto claim 11, wherein the hose is fixed in a bottom of the rim and has atleast one opening facing towards the wheel cavity.
 17. Device accordingto claim 6, wherein the wheel has a tread surface and an opposing innerside and the channel-shaped arrangement is a channel arranged on theopposed inner side of the tread surface and extending around essentiallythe internal circumference of the whole of said opposed inner side. 18.Device according to claim 6, wherein the channel is integrated in thetire.
 19. Device according to claim 6, wherein the channel-shapedarrangement is a channel in a bottom of the rim and extends aroundessentially the whole of the circumference of the bottom of the rim. 20.Device according to claim 19, wherein the channel comprises at least onewall extending from the bottom of the rim and a cover which covers thespace which is formed between said wall and a side of the rim. 21.Device according to claim 20, wherein the rim has spokes and at leastone of the spokes has a cavity forming a resonator with an openingfacing towards the wheel cavity.
 22. Device according to claim 6,wherein the resonator is integrated in the rim.
 23. Device according toclaim 5, wherein the wheel comprises a tire and a rim, wherein the rimhas two external sides facing away from the tire and a rim with twointernal sides facing towards the tire, and the rim in at least one ofits internal sides is provided with at least one cavity shaped as aresonator with an opening facing towards the wheel cavity.